Thanks to Uwe Dittes and his excellent handbook at http://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/e0fbaa71-cd8d-2910-5982-e30626035400 I was able to test and develop a single signature on a document in a very few minutes.
This is a short list of necessary operations:
Build a table for metadata using as key a field referring to data element SIGN_GUID_22 and the complete key for your to-be-signed document; in my case:
Build a structure for operation log: ZZAPT_SIGNATURE_LOG
Launch the following transactions(very intuitive):
SLG0: declare a sub-object under CDSG1
SIGNA:declare your application
SIGNO:insert the signature object
ELSIG03N: choose and link the type of signature(in my case R/3)
In this case the reference to the signed documents will be stored into the table ZZAPTSIGNATURE with the relative signature.
You can use the method if_ds_sign->get_steps_with_doc to retrieve data of your signed document(the original signer, date and time of the signature process and so on).